\version "2.19.10"

% Create a new xxxStaff and xxxVoice contexts with specified settings,
% derived from specified yyyStaff and yyyVoice contexts.

% TODO:
%
% 1) make \addLyrics smarter so that it could be used here (see test below)
%
% 2) remove code duplication; general cleanup.

newLayoutInstrument =
#(define-scheme-function
  (parser location name parent-name group-name staff-settings voice-settings)
  (string? string? string? ly:context-mod? ly:context-mod?)
  (let* ((staff-name (string-append name "Staff"))
         (voice-name (string-append name "Voice"))
         (parent-name (if (string=? parent-name "default") "" parent-name))
         (parent-staff-name (string-append parent-name "Staff"))
         (parent-voice-name (string-append parent-name "Voice")))
    (ly:parser-define! parser '$defaultlayout
      #{
        \layout {
          \context {
            $(module-ref (current-module) (string->symbol group-name))
            \accepts #staff-name
          }
          \context {
            $(module-ref (current-module) (string->symbol parent-staff-name))
            \name #staff-name
            \alias #parent-staff-name
            % is it possible to make it accept Voices of derived instruments?
            \accepts #voice-name
            \defaultchild #voice-name

            #staff-settings
          }
          \context {
            $(module-ref (current-module) (string->symbol parent-voice-name))
            \name #voice-name
            \alias #parent-voice-name

            #voice-settings
          }
        }
      #})
    ;; UGH! code duplication!
    (ly:parser-define! parser '$defaultmidi
      #{
        \midi {
          \context {
            $(module-ref (current-module) (string->symbol group-name))
            \accepts #staff-name
          }
          \context {
            $(module-ref (current-module) (string->symbol parent-staff-name))
            \name #staff-name
            \alias #parent-staff-name
            % is it possible to make it accept Voices of derived instruments?
            \accepts #voice-name
            \defaultchild #voice-name

            #staff-settings
          }
          \context {
            $(module-ref (current-module) (string->symbol parent-voice-name))
            \name #voice-name
            \alias #parent-voice-name

            #voice-settings
          }
        }
      #})))


% define "instruments" - one generic and another one derived:

\newLayoutInstrument "Vocal" "default" "ChoirStaff"
\with {
  \consists "Ambitus_engraver"
  instrumentName = "Vocals"
  shortInstrumentName = "Voc."
  \dynamicUp
  \tupletUp
  \remove "Staff_performer"
}
\with {
  \consists "Staff_performer"
  midiInstrument = "voice oohs"
}

\newLayoutInstrument "Soprano" "Vocal" "ChoirStaff"
\with {
  instrumentName = "Soprano"
  shortInstrumentName = "S"
  \clef G
}
\with { }


% test:

\score {
  <<
    \new SopranoVoice = sop \relative f' {
      c f c' f
    }
    % replacing this with \addlyrics { la la la la }
    % results in ordinary Voice being created (instead of SopranoVoice)
    \new Lyrics \lyricsto sop { la la la la }
  >>
  \layout {
    \override Staff.Stem.thickness = 4
    \override VocalStaff.Stem.color = #blue
    \override SopranoVoice.NoteHead.color = #green
  }
  \midi {
    \set SopranoVoice.midiInstrument = "clarinet"
  }
}